A communication system is a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, data, multimedia and so on.
Communication systems proving wireless communication for user terminals or other nodes are known. An example of a wireless system is a public land mobile network (PLMN). A PLMN is typically a cellular system wherein a base transceiver station (BTS) or similar access entity serves user equipment (UE) such as mobile stations (MS) via a wireless interface between these entities. The operation of the apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected. One or more gateway nodes may also be provided for connecting the cellular network to other networks, such as to another cellular system or to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks. The communication between the user equipment and the elements of the communication network can be based on an appropriate communication protocol, such as the session initiation protocol (SIP).
A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment or terminal is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based needs to be defined to enable communication by means of the system.
The communication systems typically have separated functions. In addition to provisioning of services for the users of the system the communication system also provides functions such as network management and configuration. In the current third generation (3G) multimedia network architectures various servers are used for handling of provision of different communication services for mobile users. An example of one of the services is the so-called IP multimedia services (IMS), defined in 3rd Generation partnership project 3GPP specifications. Among other functions, these servers provide call state control functions (CSCFs). A call state control function entity may provide functions such as serving call state control (S-CSCF), proxy call state control (P-CSCF), and interrogating call state control (I-CSCF). Control functions may also be provided by entities such as a home subscriber server (HSS) and various application servers. The HSS is typically for storing permanently the user's (subscriber's) profile.
In order to be able to request for a service from a communication system a user needs to be registered in the system in a serving control entity such as the S-CSCF. A user may register via an access entity of the communication system. In addition to the serving control entity, the user may need to be associated with a proxy control entity, such as the P-CSCF. The proxy entity is assigned to an area within which the user has roamed. For a more general case, when a user accesses the network through an arbitrary type of access network it can be assumed that the access network assigns a proxy control entity for controlling the accessed services from that network point of view, e.g. for bandwidth management.
It shall be appreciated that the term “session” used in this document refers to any communication a user may have such as to a call, data (e.g. web browsing) or multimedia communication and so on.
In IMN (IM network) using SIP, charging is started when the 200 OK message is processed by the S-CSCF for the called party. However this has the following problem. The 200 OK message may not be received by the caller. This may for example be because the next hop CSCF fails, the user equipment of the calling party goes out of coverage, etc. In such cases the session set-up fails and it should not be charged. However, the current standardization proposals have not recognized this as a problem and in fact with the current proposals a caller could be charged for a session, which is unsuccessful.
In more detail, the current standardization proposals define the charging records as being created (that is charging is caused) when the 200 OK message is processed by the S-CSCF of the called party. In cases where the session set-up fails, there is no mechanism for canceling the charging information.
It shall be appreciated that although the above discussed problems relate to IMS in third generation (3G) communication systems, similar disadvantages may be associated with other systems as well and thus the description is not limited to these examples.